Field of the Invention
The present disclosure relates to photoconductors and electrophotographic methods, electrophotographic apparatuses, and electrophotographic process cartridges using the photoconductors.
Description of the Related Art
Images output by electrophotographic methods using electrophotographic apparatuses are formed by subjecting photoconductors (also referred to as electrophotographic photoconductors, electrostatic latent image bearers, and image bearers) to a charging step, an exposing step, a developing step, a transferring step, etc. In recent years, organic photoconductors using organic materials are widely used as photoconductors with such advantages as flexibility, thermal stability, a film forming property, etc.
The mainstream type of recent organic photoconductors are functionally-separated laminated photoconductors obtained by laminating a charge generating layer containing a charge generating substance and a charge transport layer containing a charge transport substance as photoconductive layers over a conductive support in order. Particularly, there have been proposed many negatively-chargeable photoconductors using a layer obtained by dispersing an organic pigment as a charge generating substance in a vapor-deposited layer or a resin as a charge generating layer and a layer obtained by dispersing an organic low-molecular compound as a charge transport substance in a resin as a charge transport layer. Further, there is also proposed a technique for providing an intermediate layer (may also be referred to as undercoat layer) between a conductive support and a photoconductive layer in order to suppress charges from being injected from the conductive support.
There is a need for organic photoconductors to have greater degrees of durability and stability along with rapid advancement in full-color, high-speed, and high-definition properties of electrophotographic apparatuses. However, through the current electrophotographic process in which charging and charge elimination are repeated, the organic material constituting the organic photoconductors undergoes a gradual change due to electrostatic loads, leading to degradation of electrophotographic properties, such as occurrence of charge traps in the layer and change of chargeability.
Particularly, degradation of chargeability due to changes of the properties of the organic photoconductor is known to have a great impact on image qualities of output images and cause serious problems such as image density degradation, background fog (may also be referred to as fogging commonly), and image nonuniformity in continuous outputting.
One contributory factor behind degradation of chargeability is considered to be functional insufficiency of the intermediate layer and deterioration of the intermediate layer due to repeated use. Generally, there is a need for the intermediate layer to fulfill simultaneously and maintain two functions including “a charge injection inhibiting function” for inhibiting charge injection from the conductive support into the photoconductive layer and “a charge transport function” for transporting charges generated in the photoconductive layer into the conductive support. However, the two functions are likely to fall into the relationship of reciprocity. Furthermore, the organic material constituting the intermediate layer deteriorates under repetitive electrostatic loads. Therefore, it is very hard for the intermediate layer to fulfill simultaneously and maintain the two functions described above for a long term.
As a method for imparting the functions described above to the intermediate layer, there are proposed methods for improving the charge injection inhibiting function using a silane coupling agent containing an amino group (see, e.g., Japanese Unexamined Patent Application Publication Nos. 08-166679 and 11-133649) and methods for adding additives such as an electron transport substance and an acceptor compound to the intermediate layer (see, e.g., Japanese Unexamined Patent Application Publication Nos. 2012-58597 and 2006-30700).
Particularly, Japanese Unexamined Patent Application Publication No. 2006-30700 proposes that an undercoat layer containing metal oxide particles to which an acceptor compound (e.g., a hydroxyanthraquinone-based compound and an aminohydroxyanthraquinone-based compound.) is attached be provided over the conductive support.
However, the hydroxyanthraquinone-based compound and the aminohydroxyanthraquinone-based compound have a high crystallinity. Therefore, when these compounds are attached to the metal oxide particles, the metal oxide particles are likely to agglomerate with each other. Hence, a dispersed state of the metal oxide particles in the intermediate layer is nonuniform. Therefore, it cannot be said that the intermediate layer has electric properties that are sufficiently stable through a long term of use.
Recent electrophotographic photoconductors have an improved wear resistance in a surface layer and a drastically prolonged durable life against a mechanical wear. However, a factor that determines the life of the electrophotographic photoconductors has become how long the electrophotographic photoconductors maintain requisite electric properties as electrophotographic photoconductors, i.e., chargeability in a dark place and a quick optical attenuating property during exposure.
As described above, there is a need for the intermediate layer to fulfill simultaneously and maintain the two functions including “the charge injection inhibiting function” for inhibiting charge injection from the conductive support into the photoconductive layer and “the charge transport function” for transporting charges generated in the photoconductive layer into the conductive support. However, there will occur a problem that traps to inhibit charge flows are increased in the layer through a long term of repeated use to raise the electric potential of an exposed portion and make it impossible to obtain a sufficient electrostatic contrast between the exposed portion and a non-exposed portion to degrade the density of output images. Further, abnormal images including a blackened background, etc. will be produced due to local leaks of charges. Through these factors, the electrophotographic photoconductors come to an end of life.